From kinds of patent databases throughout the world, many patent documents related to automobile tire pressure sensing device can be searched out. The technical solutions disclosed in these patent documents may differ from one another. The sensing devices manufactured according to these technical solutions however, suffer from the problem such as big size of the sensing device in particular big size of the sensing device in radial direction due to connection among various components and limitation of the nature of the components. Consequently these sensing devices fail to have their application in all kinds of automobile. As a result, a prior art external tire pressure sensing device is mounted generally onto the tire with big size (for example the tire of a truck). In case that the sensing device is installed into a small-sized car, the sensing device will look big in size. Specifically, the dimension of the sensing device will beyond the distance between the gas nozzle shaft and the outermost rim of the hub of the car. In this case, the sensing device will be exposed out of the outermost plane of the tire, and is susceptible to collision damage caused by obstacle or person, thus resulting in malfunction of the sensing device.
The undue big dimension of the sensing device may be resulted from axial dimension and radial dimension of the sensing device. It is because normally the gas nozzle is angled with respect to the outer side surface of the tire and correspondingly, the sensing device installed on the gas nozzle is also angled outwardly. In this case, the axial height and radius of the sensing device itself together determine the offset distance of the sensing device from the plane defined at the outermost side of the tire. Apparently, the size of the sensing device may be reduced either by reduction of the radial size or by reduction of the height of the sensing device. To this end, the internal construction of the entire sensing device should be optimized. By now, on one hand, all prior art technology fail to realize this object, as it is not easy to arrange many components and electrical elements inside extremely limited internal space of the sensing device. On the other hand, sealable venting construction, which is formed by lamination of multiple separate components, also makes it impossible to further reduce the axial size of the venting construction.
A typical external tire pressure detection transmitter is disclosed in Chinese Patent No. 2826556. The transmitter contain complex components such as the printed circuit board disposed on the upper portion of a button battery for mounting an antenna thereon, the circuit board disposed on the lower portion of the button battery, and the gas-conducting construction constituted by multiple complicated and separate components. This of course increases the axial height of the transmitter. In addition, kinds of wire conduits for realizing electrical connection among the components arranged axially also necessarily increase the radial dimension of the transmitter. Clearly, the external tire pressure detection transmitter made according to the above technology is large in size and can only find its application in large-sized truck tire. Though it can also be mounted in a normal car, it will be susceptible to damage problems discussed above. Other patent documents searched out by the inventor also suffer from the same problem.
It is apparent from the above analysis that conventional physical construction doesn't work to significantly reduce the size of the external tire pressure sending device, thus failing to be mounted into tire of all kinds of automobile.